<!DOCTYPE html>
<html lang="en">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    * {
      margin: 0;
      padding: 0;
      list-style: none;
    }

    .box {
      margin: 100px auto;
      width: 640px;
      height: 640px;
      transition: all 30s linear;
    }

    .box:hover {
      transform: rotate(3600deg);
    }

    .box>li {
      float: left;
      margin: 10px;
      width: 300px;
      height: 300px;
      background-color: skyblue;
    }

    .item1,
    .item4 {
      border-radius: 0 100%;
    }

    .item2,
    .item3 {
      border-radius: 100% 0;
    }
  </style>
</head>

<body>
  <ul class="box">
    <li class="item1"></li>
    <li class="item2"></li>
    <li class="item3"></li>
    <li class="item4"></li>
  </ul>
</body>

</html>